Or: The auxiliary engines have tripped. There is a blackout. The emergency generator starts up and comes on load. The emergency lighting comes on. Engineers are working to restart the auxiliary engines. After a few minutes, the emergency generator stops, throwing the engine room into darkness.
Most companies and vessels have procedures in place to monitor fuel quality. Close attention is paid to fuel management of both residual fuels and distillate fuels as this has a direct impact on safety, health and environment as well as on the economic operation of vessels.
However, not much attention appears to be being paid to the quality of fuel being used for emergency equipment like emergency generators, life boat engines and emergency fire pumps.
Cold Flow Properties
The emergency equipment fuel oil should be suitable for operation at the minimum anticipated operating temperature without heating. There are three parameters which measure cold flow properties of a fuel.
The Cloud Point (CP) of a distillate fuel is the temperature at which wax or other solid substances begins to separate from petroleum oil. When a sample of distillate fuel is cooled at a specified rate and examined periodically the temperature at which haziness is first observed at the bottom of the test jar is recorded as the cloud point.
The Cold Filter Plugging Point (CFPP) is the lowest temperature at which the fuel will pass through a filter under specified conditions.
The Pour Point(PP) is the lowest temperature at which the fuel will flow.
The CFPP and PP can be reduced by the use of additives but CP cannot be modified using additives. Hence even though a distillate may have a very low PP, the CP may in fact be high.
Fuels stored at temperatures below the pour point may cause filter problems and solidify completely. Usually the CP and CFPP of a distillate fuel are a few degrees higher than the PP. Hence it is generally recommended that storage temperature should be at least 10oC above PP. However if Pour Point Inhibitors or Cold Flow Improvers (CFI) have been used to reduce the pour point to meet the PP specification, CP may be more than 10oC higher than the PP. In these cases the rule of the thumb of satisfactory storage temperature at least 10oC above PP would not apply. When the fuel temperature drops to or below the cloud point, wax crystals start to form which will cause filter clogging, resulting in fuel starvation and engine stoppage. The wax crystals will disappear when the temperature increases above the CP temperature. This would be an issue if vessels are in colder climes with ambient temperatures approaching the CP. It would not be possible to run the emergency equipment like emergency generator, life boat engine and emergency fire pump, if engine driven, in these conditions.
CFIs can also cause operational problems. CFI chemicals can be preferentially adsorbed by some filter materials, causing them to appear blocked. Also, the CFPP test rig has a filter gauze with a pore size of 43 µm. A CFI additive may enable the fuel to pass the CFPP limit, but if the fuel system is fitted with 10 µm filters the fuel could still block the filter.
Most operators are well informed of the common residual and distillate grades in the ISO8217 Marine Fuel Specifications. However not many are familiar with the grade DMX in Table 1 – Distillate Marine Fuels.
When comparing the distillate grades, the major differences of the DMX grade with the other distillate grades are found to be in the parameters Flash point, CP and PP:
| Parameter
| Unit
| Limit
| DMX
| DMA
| DMZ
| DMB
| Test Method
|
| Flash point
| °C
| Min
| 43,0
| 60,0
| 60,0
| 60,0
|
|
| Cloud point
| °C
| Max
| -16
| —
| —
| —
| ISO 3015
|
| Pour point (upper)d
| °C
| Max
| -
| −6
| −6
| 0
| ISO 3016
|
| d. Purchasers should ensure that this pour point is suitable for the equipment on board, especially if the ship operates in cold climates.
| |||||||
Fuels used for emergency equipment require good cold flow properties in order to ensure operation in cold climes. The grade DMX is meant for use in emergency equipment and has a maximum Cloud Point requirement of -16°C.
The Flash Point (FP) of fuels with low CP would be lower than 60°C. This is the reason use of fuels with a minimum Flash Point of 43°C is permitted for use in emergency equipment only. DMX is the only grade in both the distillate and residual fuel tables which has a minimum Flash Point limit of 43°C.
DMX has a CP requirement of -16°C maximum while the grades DMA and DMZ only specify a pour point requirement of -6°C maximum for winter quality grades.
Distillate grades other than DMX do not specify a maximum cloud point requirement. Till Cloud Point is included in the ISO 8217 requirements, it is recommended that additional cloud point testing be carried out for all distillate samples.
The grade DMX is meant specifically for use in emergency equipment. However the use of this fuel grade is not mandatory. This grade is not easily available. Very often, the operational area and conditions the vessel is likely to operate in is not taken into consideration and DMA grade MGO which may not have good cold flow properties is used instead for the emergency equipment. Vessels which have been operating for many years in a warm temperate climate may have to suddenly proceed to a cold area. The emergency equipment fuel tanks may contain fuel which is not suitable for cold weather operation. This could have disastrous consequences as it would not be possible to run the emergency equipment in colder climes. For satisfactory cold flow properties, a CP of around 3 to 6°C below the lowest temperature the vessel is likely to operate in is recommended.
Fuel Contamination
As fuels in the emergency equipment storage tanks remain unused for long periods of time, their quality may deteriorate due to the following:
- Water(condensation/contamination)
- Growth of microorganisms like bacteria, yeast and fungi
- Oxidation Stability
- Presence of Fatty Acid Methyl Esters (FAME)
Water can be present in the fuel tanks. Often water enters the tanks through condensation. Given the correct conditions in fuel storage systems micro-organisms can grow and multiply. Bacteria, fungi and yeast are living organisms which may be present in fuel storage tanks and in particular where water is allowed to build up. Distillate fuels are more prone to bacterial infection. Microbial infection can lead to slimy deposits in tank bottoms, plugging of filters, pitting corrosion on fuel tank bottoms or at oil water interface and injector fouling.
Due to the practice of blending FAME into automotive diesel and heating oil, it is almost inevitable that some distillates supplied in the marine market contain FAME. FAME can lead to potential complications with respect to storage and handling in a marine environment, due to its tendency to oxidation, long-term storage issues, affinity to water and risk of microbial growth, degraded low-temperature flow properties and FAME material deposition on exposed surfaces, including filter elements.
Straight run MGO is generally very stable as it contains very small amounts of unsaturated hydrocarbons. However, due to the increased demand, most of the MGO in the market now contain cuts from cat crackers, visbreakers and cokers which are unstable if they have not been hydrotreated. This could lead to oxidation during storage and eventually to plugging of filters when the fuel is used.
Though the emergency equipment engines must be tried out weekly (SOLAS regulation 20 paragraph 6.2), they are usually only run for short periods of time. Consumption may not be much and fuel starvation due to any of the above mentioned issues may not manifest itself during these short periods.
It is a matter of concern that hardly any fuel samples from emergency equipment are being tested. This indicates a false sense of security. Engines may fail to operate when they are needed most in emergencies similar to the ones mentioned in the beginning of the article. Elementary precautions should be taken like ensuring fuels used in emergency equipment are fit for purpose and the quality of the fuel in the storage tanks is regularly monitored by periodic testing every six months.
Thomas Tampi is station manager, Fujairah, at Veritas Petroleum Services. Email: [email protected]
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